1. Field of the Invention
The present invention relates to a method for producing a single crystalline semiconductor film formed on an insulation base member for fabricating an electronic circuit thereon, which film is constituted from so called SOI (Silicon on Insulator) structure made from a single crystalline silicon film. More particularly, the invention relates to a semiconductor film producing method which is so called a recrystallization method in general.
The single crystalline silicon film produced in accordance with the present invention can be applied to various electronic devices, such as an active matrix liquid crystal display device, a high density LSI, a high dielectric breakdown device, a radiation proof device, and a three-dimensional integrated circuit.
2. Description of the Related Art
The SOI structure can be made by various methods such as a recrystallization method, an epitaxial growth method, an insulation layer embedding method, and a laminating method. Such SOI structure forming techniques in general are disclosed in detail in "SOI Structure Forming Technique" issued from Sangyo Tosho Co., Ltd., 1987.
As one of the recrystallization methods, a laser beam recrystallization method has been used, wherein a polycrystalline or amorphous silicon film formed on an insulation base plate is molten by using laser beam energy and wherein crystal is grown in the molten portion while moving the portion.
There have been made various attempts to improve the temperature distribution in the film to be irradiated by the laser beam to form a single crystalline film as follows.
One of the attempts is such that a plurality of laser sources are arranged to improve the temperature distribution in the laser spot.
Another attempt is such that an antireflection film or an optical absorption film is formed on the film sample surface to change the absorption ratio of the laser beam so as to improve the temperature distribution in the film.
A further attempt is such that the structure of the sample is constructed so that the heat radiation therefrom is changed spatially so as to improve the temperature distribution in the film.
In accordance with the laminating method, the film of SOI structure is formed in such a way that a pair of single crystal silicon substrates each having an oxide film formed thereon are faced together with the oxide films thereof being sandwiched and in contact with each other between the substrates, and that the substrates are heated to about 700.degree. C. in an oxidation atmosphere so as to bond the substrates together, and after that one of the substrates is etched to a predetermined thickness by an etching back method.
In the event that a silicon film is formed on a glass plate or an insulation film and that the silicon film is molten and recrystallized to form a single crystal film thereon, due to that there are no seed portions for the single crystal in the film, the crystal axes of the single crystal film are uncontrollably rotated so that it becomes difficult to obtain a single crystal film having a desired crystal axis orientation.
With regard to the laminating method, when the dry etching process is adopted to etch the silicon substrate, the etching time is elongated, resulting in the reduction of through-put and the element forming surface is damaged. On the other hand, when the wet etchin process is adopted to etch the silicon substrate, evenness of the film thickness is impaired and it becomes necessary to arrange a mask on the other silicon substrate not to be etched.